Summary An Air Canada Jazz Canadair CL600-2B19 (serial number7058, registration C-FSJJ) being operated as JZA8954 was on a scheduled flight from Toronto, Ontario, to Fredericton, New Brunswick. While in cruise at flight level330, the flight crew observed the cabin altitude climbing at a rate of approximately 1000feet per minute. A descent clearance to flight level250 was requested from Moncton Area Control Centre and, after the aircraft was level at flight level250, a continued increase in cabin altitude was observed. The crew requested and received clearance for further descent to 9000feet. The pilots donned their oxygen masks during the descent as the cabin altitude climbed through 10000feet. When the cabin altitude reached 14000feet the passenger oxygen masks automatically deployed. The aircraft was leveled at 9000feet where it remained until descent for final approach was initiated. The aircraft landed at Fredericton without further incident at 2115coordinated universal time. There were no injuries to the 50passengers and 3crew members. Ce rapport est galement disponible en franais. Other Factual Information Modern commercial aircraft that are designed to conduct sustained flight above 10000 feet are pressurized. The pressurization systems are automatically controlled to maintain cabin altitudes below 10000feet in order to provide a safe and comfortable environment for the passengers. As the aircraft climbs, its pressurization system pumps air into the fuselage to maintain a cabin pressure altitude below 10000feet. This results in a higher pressure inside the aircraft than that of atmospheric pressure outside. The resulting pressure differential is regulated by the aircraft system. Before the pressure loss started, C-FSJJ was level at flight level(FL)330 while maintaining a cabin altitude below 10000feet. The aircraft had been established in level cruise flight for approximately 16minutes before the crew detected a cabin pressure variation. Although there were no aircraft system warnings or caution messages present on the engine indicating and crew alerting control system (EICAS), the crew noticed that the cabin altitude was climbing at approximately 1000feet perminute. On checking the air conditioning control panel, it was observed that the left air conditioning unit (ACU) pack was on-line. However, the right ACU pack was off-line. The bleed air control panel was indicating that the right 10thstage bleed shut-off valve (SOV) was also off-line. Therefore, the left ACU pack was the only available source of pressure for the air conditioning and pressurization demands of the aircraft. If oneof the twoACU packs goes off-line, the remaining pack will automatically switch to Hi flow as a normal function of the system. This should ensure cabin pressure can be maintained at an altitude below 8000feet. The maximum aircraft altitude for single-pack operation is 25000feet. After receiving clearance from Moncton Area Control Centre (ACC), the crew expedited descent with the intent of leveling off at FL250 before the cabin altitude could reach 10000feet. During the descent, the crew attempted to reset both the right 10thstage bleed SOV and the right ACU pack but neither would come back on-line. Once the descent from FL250 was initiated, the captain made an announcement informing passengers that one of the ACU packs was not operating and that the flight was continuing on to destination. Approximately one minute after descent was initiated, the master warning illuminated for twoseconds and the cabin altitude warning came on. The crew then observed "DISPLAY COOL" and "AIRINC COOL" messages on the EICAS primary display. During the descent from FL250, the cabin altitude warning activated indicating that the cabin altitude had reached 10000feet. At this time the flight crew donned their oxygen masks. Despite an average rate of descent of 4000feet per minute, the cabin altitude climbed steadily until it reached 14000feet. At that point the passenger oxygen masks deployed automatically. The cabin altitude warning extinguished after the aircraft descended below 10000feet. After the aircraft was level at 9000feet, the flight crew ran through the associated checklists and noticed that the pressurization fault light was illuminated on the pressurization panel. The crew then selected manual pressurization mode. Sevendays earlier, the aircraft was reported to have had poor airflow. Ground runs were completed by the maintenance personnel; the airflow was reported as normal. Following the occurrence flight, a maintenance inspection revealed several separate anomalies related to both the left and right air conditioning systems: The left system, air supply duct (part number601R95211-113), was found detached from its flange at the water separator joint. The duct is located in the unpressurized tail section of the aircraft, aft of the pressure vessel. The detached flange created a leak through which an undetermined percentage of air pressure was lost. The right system pressure regulating shut-off valve (PRSOV) sense line was found detached, which effectively caused that system to go off-line. Both the right and left system bulkhead check valves (part number92E20-4) were missing a return spring. The missing return springs would permit the check valves to remain open and allow cabin air to backflow and escape through the duct system in the event of a breach in the respective ducts between the PRSOV valves and the pressure bulkhead. The missing springs were not located. The duct flange failure observed in the left system was similar in nature to previous duct failures experienced in the air supply systems of the CRJ100/200series aircraft. Those duct failures are the subject of an airworthiness directive (CF-2003-05R1). However, those ducts are of a different part number and location within the air supply system than the duct that was found detached on C-FSJJ. Transport Canada Airworthiness Directive (AD) CF-2003-05 "Air Supply Ducts and Bulkhead Valve Inspections" was issued on 04February2003; this was later superseded by CF-2003-05R1 issued on 31March2006. The background section of the AD indicates the following: Technical records indicated that no recent maintenance had been carried out on the PRSOV line. The investigation could not determine how the line became loose and detached. It should be noted that as part of ADCF-2003-05R1, Bombardier added a new task to the CRJ maintenance program. The task calls for a repeat check valve inspection at an interval of 4000flight hours. Prior to this incident, the check valves (part number 92E20-4) were last inspected at the operator facilities on 08August2005; the springs were present and deemed serviceable.